We propose to study, during and after partial acclimatization to high altitude, the effects of hypoxia upon: (1) fluid and electrolyte content of red cells and striated muscle cells; (2) fluid compartments and volumes; (3) hormones such as ADH, renin, and aldosterone in blood and urine; which influence and in turn are influenced by these volumes; (4) the microvascular circulation of retinae and conjunctivae; and (5) the circulatory and pressor amine response to hand grip exertion. We expect to show an orderly inter-relationship between changes in hormone secretion and distribution of fluid in body compartments, which we hope to be able to relate to the microvascular and circulatory changes. The changes observed during and after partial acclimatization are the resultants of responses to hypoxia and hypocapnia; we expect to distinguish which of these is most influential. We will attempt to correlate these changes with those seen at low altitude in patients with a range of disorders associated with hypoxia.